The present invention relates to a semiconductor integrated circuit and an operation method for the same, in particular, to technology which is useful for performing temperature control or temperature monitoring outside a semiconductor integrated circuit which has a built-in functional module with a large operating current and a built-in temperature detection circuit to detect chip temperature and which is influenced greatly by the noise of a system board.
Document 1 in the following describes the outline of a semiconductor integrated circuit working as a precision digital thermometer (product name MAX1617) which reports the temperature of both a remote sensor and its own package. A diode-connected transistor as a remote sensor and a 2200 pF noise filtering capacitor are coupled in parallel to two external input terminals of the semiconductor integrated circuit. One external input terminal of two external input terminals functions as a current source of the remote sensor and a non-inverted input terminal of an A/D converter. The other external input terminal of two external input terminals functions as a current sink of the remote sensor and an inverted input terminal of the A/D converter.
Inside the semiconductor integrated circuit of the product name MAX1617, a first variable current source is coupled between power supply voltage Vcc and the one external input terminal, and a first diode is coupled between the other external input terminal and ground voltage. Also inside the present semiconductor integrated circuit, a second variable current source, a second diode, and a third diode are coupled in series between the power supply voltage Vcc and the ground voltage. Therefore, a first current flows from the power supply voltage Vcc toward the ground voltage through the first variable current source, the remote sensor, and the first diode; and a second current flows from the power supply voltage Vcc toward the ground voltage through the second variable current source, the second diode, and the third diode. Remote voltage between both ends of the remote sensor and local voltage between both ends of the second diode are supplied to an input of the A/D converter through a multiplexer. An output of the A/D converter is coupled to an input of a remote temperature data register and an input of a local temperature data register.
The remote temperature data register, a high remote temperature threshold data register, and a low remote temperature threshold data register are coupled to a remote digital comparator. The local temperature data register, a high local temperature threshold data register, and a low local temperature threshold data register are coupled to a local digital comparator. An output of the remote digital comparator and an output of the local digital comparator are supplied to a set input terminal of a flip-flop through an OR gate. An output signal of the flip-flop is supplied to a gate of an output MOS transistor. An open drain of the output MOS transistor functions as an alert output which enables interruption to a micro controller.
Document 2 in the following describes an outline of a semiconductor integrated circuit of a product name LM89 which is analogous to the semiconductor integrated circuit of the product name MAX1617 described in Document 1. A diode-connected transistor as a remote diode and a capacity of 2.2 nF are coupled in parallel to two external input terminals of the analogous semiconductor integrated circuit. The present semiconductor integrated circuit accurately measures its own temperature as well as the temperature of an external device. Inside the semiconductor integrated circuit, two external input terminals to which the remote diode is coupled are coupled to an input of a signed 10-bit Δ-S A/D converter through a local/remote diode selector and a temperature sensor circuit.
An output of the signed 10-bit Δ-S A/D converter is supplied to one input terminal of a first comparator, one input terminal of a second comparator, and one input terminal of a third comparator, through a filter. A high temperature limit register is coupled to the other input terminal of the first comparator, a low temperature limit register is coupled to the other input terminal of the second comparator, and a temperature critical-limit and hysteresis register is coupled to the other input terminal of the third comparator. Outputs of the first comparator, the second comparator, and the third comparator are supplied to a set input terminal of a flip-flop, and an output of the flip-flop is supplied to a gate of a first output MOS transistor. An open drain of the first output MOS transistor functions as an alert output. The alert output is activated when temperature goes outside a programmed window set up by the high temperature limit register and the low temperature limit register or exceeds the programmed critical limit. The output of the third comparator is also supplied to a gate of a second output MOS transistor, and an open drain of the second output MOS transistor functions as a temperature critical alert output. When the temperature exceeds the programmed critical limit, the temperature critical alert output is activated. A shutdown control input terminal of a main power supply responds to the activated temperature critical alert output, and the main CPU voltage, supplied from the main power supply to a processor which has the built-in remote thermal diode, is shut down.
On the other hand, Document 3 in the following describes a temperature detection circuit which is preferred for a CMOS process, and which generates band gap reference voltage Vbgr of low temperature dependence and a temperature detection signal Vtsense of which the temperature gradient can be set arbitrarily. The present temperature detection circuit is composed of a band gap generating part and an amplification/feedback part. The band gap generating part includes a first and a second transistor, and a first through a fourth resistor. The amplification/feedback part includes a CMOS differential amplifier circuit. In the band gap generating part, collectors of the first and the second transistor are coupled to power supply voltage through the first and the second resistor, respectively. An emitter of the first transistor is coupled to one end of a third resistor and the fourth resistor coupled in common. The other end of the third resistor is coupled to an emitter of the second transistor, and the other end of the fourth resistor is coupled to the ground voltage.
Emitter current density of the second transistor is set smaller than emitter current density of the first transistor. Collector voltage of the first transistor detected by the first resistor, and collector voltage of the second transistor detected by the second resistor are respectively supplied to difference input terminals of the CMOS differential amplifier circuit. An output signal of the CMOS differential amplifier circuit is fed back to a base of the first transistor and a base of the second transistor. Band gap reference voltage Vbgr is given by the sum of base-emitter voltage Vbe of the first transistor and the voltage drop of the fourth resistor, where the voltage drop of the fourth resistor is determined by the sum of the emitter current of the first transistor and the emitter current of the second transistor. A temperature detection signal Vtsense is set up by a voltage drop of the fourth resistor which is determined by the sum of the emitter current of the first transistor and the emitter current of the second transistor.
In a chip of a system LSI, the temperature detection circuit described above, CPU, RAM, a clock generation circuit, an input/output interface, and an analog buffer circuit are integrated. The temperature detection signal Vtsense generated in the temperature detection circuit is transferred to an A/D converter provided outside the chip through the analog buffer circuit, and the converted digital information from the A/D converter is supplied to CPU through the input/output interface. By referring to the converted digital information and a table which is determined in advance and indicates the preferred relationship between temperature and a clock frequency, CPU generates a clock control signal to supply to a clock generation circuit. For example, when temperature becomes higher than a constant value, the frequency of an operation clock is decreased, and the electric current consumption is reduced; accordingly, the temperature is lowered. On the contrary, when the temperature becomes lower than a constant value, the frequency of the operation clock is increased, and the electric current consumption is increased to gain the operating speed.
(Document 1) Product name MAX1617, data sheet: “Remote/Local Temperature Sensor with SMBus Serial Interface”, pp. 1-20, http://datasheets.maxim-ic.com/en/ds/MAX1617.pdf (Searched on Mar. 31, 2008)
(Document 2) Product name LM89, data sheet: “±0.75° C. Accurate, Remote Diode and Local Digital Temperature Sensor with Two-Wire Interface”, pp. 1-20, http://cache.national.com/ds/LM/LM89. pdf. (Searched on Mar. 30, 2008)
(Document 3) Japanese Patent Application Laid-open No. 2006-286678.